The present invention relates generally to ground proximity warning devices and more particularly to systems and methods for enabling such ground proximity warning devices in rotary wing aircraft.
Ground proximity warning systems provide aural and visual warnings of aircraft descent after takeoffs, landings, during a go-around after a missed approach and other low altitude flying conditions. These systems typically detect altitude loss by computing the barometric altitude (MSL) rate change. The radio altitude or altitude above ground level (AGL) is then determined with a radio altimeter. The warning device typically issues a number of aural or visual warnings if the altitude loss is excessive for the radio altitude at which the aircraft is flying. For example, one such system, compares the accumulated altitude loss after takeoff of the aircraft, and generates a warning if the altitude loss exceeds a predetermined value before a threshold altitude has been reached. Examples of such a system are disclosed in commonly assigned U.S. Pat. Nos. 3,946,358, 3,947,808 and 4,818,992, the complete disclosures of which are incorporated herein by reference. Another type of warning system warns the pilot in the event that the aircraft if descending too rapidly, particularly on approach to a landing. Examples of this type of warning system are disclosed in commonly assigned U.S. Pat. Nos. 3,958,358 4,215,334 and 4,551,723, the complete disclosures of which are also incorporated herein by reference.
The present invention is particularly concerned with ground proximity warning devices for rotary wing aircraft, such as helicopters. Most conventional ground proximity warning systems are designed to operate with transport aircraft, particularly with large turbine powered aircraft, such as those flown by commercial airlines. Since rotary wing aircraft are highly maneuverable, they typically have flight operational characteristics entirely different than that of transport aircraft. Consequently, the systems designed for transport aircraft can generate nuisance warnings during certain normal operational conditions in rotary wing aircraft. In addition, these warning systems may provide no warning or an inadequate warning during other flight conditions. Thus, a pilot may tend to ignore the warnings provided by such systems, rendering them ineffective.